Saw an article about the SU57 and they were saying -- yeah, there are big gaps so the stealth is compromised but the Russians probably don't care. (or possibly (IMHO) it's early days, or maye they can't do better).

Then they started talking about 2 radars one on each side. The claim was that they could fly parallel to US stealth fighters and launch missiles from the side. They said that this type of approach would be ignored due to the the design of US sensors.

Sounded pretty bizaare, but I wondered if there was even a timy amount of truth there.

ford2go wrote:Then they started talking about 2 radars one on each side.

Side array of Su-57 has 357 T/R modules , for comparison, fire control radar of F-16, the APG-80 has more than 1000 T/R modules. So that kind of radar would be totally useless against stealth aircraft, they won't even detect legacy aircraft from a significant distance. Then launching missiles to target at the side will result in much shorter range, and your IR signature will be much bigger too (because you exposes your engine nozzle and plumes).

ford2go wrote:The claim was that they could fly parallel to US stealth fighters and launch missiles from the side. They said that this type of approach would be ignored due to the design of US sensors

They're talking about beaming (a similar concept is called notching). I may massacre the explanation, basically the idea is that pulse doppler radars filter out signals which seem to be moving below a certain threshold speed, such as the ground, to eliminate clutter. So if you fly (almost) perpendicular to a target, and your closing speed relative to that target is similar to that of the ground to that target, then the target's radar filters you out thinking that you're part of the ground.

Therefore, the sideways radars allow the Su-57 to keep a target on its radar, while the Su-57 itself will disappear from the target's radar, when the Su-57 flies (almost) perpendicular to the target. That's the theory. Other aircraft wouldn't be able to do this because their radars only face forward, not to the side.

The problem with that is modern radars have more sophisticated signal processing techniques. I mean, modern radars can even map out the ground in 3D (SAR). So presumably it's not that difficult to code in some processing logic like "filter out ground stuff EXCEPT if it's above the horizon or if its elevation is above X feet", basically ways to not erroneously filter out planes when filtering out ground clutter. So I wouldn't bet on it working against modern radars, such as the AESA radars of the F-22 and F-35, where it's all about good signal processing.

The side radars are relatively small, so they only have maybe 1/3 the range of the normal nose radar. There's not even much evidence in public literature that the normal nose radar can even detect stealth aircraft at appreciable distances (i.e. say over 40 miles away, just making up a distance), when modern radars can detect non-stealth targets from over 100 miles away, so it's unclear if the side radars will be of much use against stealth aircraft.

As an aside, the Eurofighter is touted as being able to gimbal its radar to the side a bit for a wider scan field (about 200 degrees compared to the typical AESA radar's 120 degrees). So it can, to a certain extent, perform the same function using its main radar.

Vanshilar, I'd say you gave pretty good explanation about the phenomena. Beaming/notching is likely close to useless tactic against modern AESA radars as AESA are far more capable of filtering clutter. AESA radars are at least couple of orders of magnitude better at filtering out targets in clutter, so trying to do beaming would be really difficult to pull off. They actually do SWT (Search-While-Track) and can do many things to maximize the chances of tracking the target no matter what it does. Beaming worked in old mechanically scanned radars because they had far less sophisticated methods to filter out targets available and basic operation is optimized for search and not tracking. It probably also worked fairly well against older SARH missiles, but I doubt it works well against modern ARH missiles that come from awkward angles and give very little warning time and can get updates from fighter radar.

I'm still waiting to hear how the Su-57s are supposed to know when to fly perpendicular flight paths, when they don't know where F-22s and F-35s happen to be. The F-22/35 would've already detected them long before they knew to start maneuvering, so the likelihood of the tactic being useful is nil.

If the software can be tuned to filter out ground clutter that is not moving, then it can be just as easily be programmed NOT to filter out airborne items that are beaming. Don't forget that if the radar/ESM even has a hint of a target, the EOTS will verify it and can easily detect (especially when cued) a fighter sized object at ~50nmi. The Block 4.1 EOTS upgrades will extend this range even further.

icemaverick wrote:What is the real purpose of the sideways radar arrays? Are they to detect incoming missiles? Are they hoping that in time they will be able to improve the detection range as the technology improves?

The only thing that is nice about the side arrays, is that it allows you to fire a missile, and then slow your closure rate, while providing 2 way datalink guidance.

icemaverick wrote:What is the real purpose of the sideways radar arrays? Are they to detect incoming missiles? Are they hoping that in time they will be able to improve the detection range as the technology improves?

The only thing that is nice about the side arrays, is that it allows you to fire a missile, and then slow your closure rate, while providing 2 way datalink guidance.

Among other things, sideways-looking arrays are terribly useful for SAR. SAR relies on the motion of the plane perpendicular to the direction of the radar beam.

icemaverick wrote:What is the real purpose of the sideways radar arrays? Are they to detect incoming missiles? Are they hoping that in time they will be able to improve the detection range as the technology improves?

The only thing that is nice about the side arrays, is that it allows you to fire a missile, and then slow your closure rate, while providing 2 way datalink guidance.

But tactics and networking offer a better solution, since the firing aircraft can turn away and his wingman that's 40nmi behind him can guide the missile using a far better forward facing radar.

Well, there's one other not-so-fancy, non-VLO related reason for side facing antennas: AESAs have a narrower field of view than mechanically scanned antennas. Side facing antennas, even if less capable, help to compensate of this, and also can allow the launching aircraft to turn further away from the target aircraft awaiting their missile's own seeker to lock on. F-22 was going to do the same thing until they were dropped (along with IRST) to reduce development costs.

Of course the following story, IF true, makes the whole thing academic (I'm going to post this elsewhere as well):